Source: Rookie C Marcus Martin to be sidelined eight weeks

Niners rookie center Marcus Martin is expected to be sidelined about eight weeks after he sustained an injury to his kneecap in Sunday’s 21-7 win over San Diego, a source said.

Martin, a third-round pick, is the second-string center behind Daniel Kilgore and is also capable of playing guard. Jim Harbaugh mentioned Adam Snyder and Joe Looney as the top candidates to assume Martin’s backup duties at center.

Snyder, 32, started three games at center for the Cardinals in 2012. Looney, who is the starter at right guard with Alex Boone in the midst of a contract holdout, has had practice time at center since he was drafted in the fourth round in 2012.

The 49ers have three options with Martin: They can place him on injured reserve; put him on injured reserve with the designation to return or carry him on the 53-man roster.

Nose tackle Glenn Dorsey (biceps), who could return by mid-November, is also a candidate to be placed on IR with the designation to return. The team can only give one player the designation each season. The 49ers can place linebacker NaVorro Bowman (knee) on the physically unable to perform list because he didn’t pass his preseason physical after he was injured in the NFC Championship Game.

Today, Jim Harbaugh declined to provide many details regarding Martin’s injury. He only offered that Martin didn’t tear his ACL and could return this season.